Final anode supply systems for cathode-ray tubes



April 16, 1963 J. D. BURKE 3,086,142

FINAL ANODE SUPPLY SYSTEMS FOR CATHODE-RAY TUBES Filed Nov. 12, 1957 70 HIGH VOLTAGE CIRCUIT RECTIFIER HEAT/N6 F/G.

CIRCUIT United States Patent 3,086,142 FINAL ANODE SUPPLY SYSTEMS FOR CATHODE-RAY TUBES John Donald Burke, 54 Hubbards Chase,

, Hornchurch, Essex, England Filed Nov. 12, 1957, Ser. No. 695,991 2 Claims. (Cl. 315-106) This invention relates to supply systems for the final anode of cathode-ray tubes.

One object of the invention is to lengthen the life of high-voltage rectifier tubes.

Another object is to increase the possible current output of such tubes, and the range of cathode-ray tube brilliance.

The problem this invention attacks is already worldwide, since television has gone into tens of millions of homes, and in many countries. Yet, every such receiver, practically, has the same inherent fault-its high-voltage rectifier tube (known also as the Extra High Tension, or E-HT, rectifier valve) is liable to have a short life. By my experience, in common with that of other technicians, the tube may fail in the first month, or six months, or at some time within the first year.

Everyone in our profession knows this. The public knows it, in part, through spending vast sums, en masse, for service calls and rectifier tube replacements. Yet, while some attempts have been made to solve the problem, as will be described later, for the most part television receivers are still being produced with a high degree of probability that their high-voltage rectifier tube will not last long.

What, then, is the difficulty? Simply this: The source of power from which both the heating current for the rectifier tube and the beam current for the cathoderay tube (after rectification) is drawn-that source is weak. It is a marvelously efiicient arrangement in most other ways, and has advanced television tremendously, but when the beam current rises, the heating current for the rectifier must fall.

Most vacuum tubes are operated within close tolerances as to their heating current. In addition to other problems, there are two major difiiculties: Overheating, which may cause the heating wire to fuse (open circuit), or it may also cause a short circuit across a portion of the heating element; underheating, which causes problems of loss of ability to emit electrons, varying according to the type of emitive material and construction.

The high-voltage rectifier tube, however, is subject to both extremesits whole life is a gamble.

A cathode-ray tube, by the nature of its task as a reproducer of pictures, must have a constantly varying beam current. For example, a black picture element may be reproduced by reduction of the beam to 50 rnicroampores; and (with the same range of contrast in use) a bright white element may be reproduced by a flow of 150i microamperes.

It is generally agreed in the industry that such a range represents so-called normal operation. If this range were all that was ever used, it is possible that high-voltage rectifier tubes could survive for long periods, for the variation of loading across the supply system would not cause the rectifier heater to vary in temperature more than its tolerance limits.

With that knowelge in hand, some manufacturers have confined the limits of operation of their receivers so as to achieve some success. For example, a voltage-sensitive metrosil, or a high-voltage regulator tube, parallels the system so that reduction of beam loading is partially offset by increased loading through the regulator. Both arrangements add to the cost and complication of manufacture, and have the limitation that they operate only on the no-beam low-beam end of the scale. If, perchance, the user turns his brightness control up high, then such arrangements as the above cannot protect the rectifier tube. It is subject to being underheated, and therefore to loss of the ability to emit electrons.

Some receivers, in view of the above, have limitations as to their maximum beam, holding the range of brightness at the command of the viewer to a lower level. One instance, which has come to my attention, Where this has been done, is by a company renting television receivers of their own design and manufacture.

Tolerance in manufacture also aggravates the problem. In this connection there is the question of variations in rectifier tubes (as betwen a number of the same type), variations in transformers, variations in other components, and the adjustment and setting of controls such as the horizontal drive control. Further, there are such problems as a free running horizontal oscillator (for example, the eifect of operation of the receiver when no synchronizing pulses are received), variations in cathoderay tube sizes, beam current characteristics, the effect of various types of deflection equipment and its adjustment, the use of boost voltage from the reclaim of fiyback ena y- Further reference to known art will be made in the description of the embodiments. Embodiments of the invention will now be described in greater detail by way of example and with reference to the accompanying drawings of which- FIGURE 1 is a schematic representation of the principle of the invention, and an electro-mechanical embodiment of the principle.

FIGURE 2. illustrates an embodiment of the invention utilizing a saturable reactor.

FIGURE 3 shows an embodiment combining electromechanical principles and saturation principles.

FIGURE 4 shows another electro-mechanical embodiment of the principle.

FIGURE 5 shows a circuit arrangement utilizing the variation of cathode-ray tube bias to control another vacuum tube whose cathode-anode current is then used to operate compensating means according to this invention.

Considering now the FIGURE 1, this drawing shows both that which is known, and .that which is new. The known features are shown is easily recognized symbolsa horizontal output tube 1, a damper 2, a high-voltage rectifier tube 3, a horizontal output transformer 4 with high-voltage overwind 5, a heater winding 6 for the high voltage rectifier, a connection 7 from said rectifiers heater 8 to the final anode 9 of the cathode-ray tube 10, a connection 11 to the cathode 12 of said cathode-ray tube, a connection 113 to the B plus supply joining the plate of the damper tube.

The new features are: The variable reactance coil 14 placed in series with the high-voltage rcctifiers heater 8 and its associated heater winding 6; the core 15 variable in relation to said coil; a dotted line '16 indicating coupling for said core to a second core 17 situate in variable relation to a second coil \18 acting as a driving coil; arrows indicating connections for said driving coil; X marks at A, B and C indicating points of insertion possibilities for said driving coil in series Wth the final anode 9 of the cathode-ray tube, the cathode 12 of said tube, or the plate of the damper tube.

If the driving coil 18 is inserted at A, the current through the coil will be beam current, that is to say, a varying direct current ranging from 0 to about 250 microamperes (plus). The same is true for insertion at B.

There are differences in design problems, however, between these two, in relation to insulation, length of leads, mounting, and video by-passing which would be desirable if the driving coil is connected at point B.

However, if the coil is inserted at C the current involved would be in the order of a hundred and more milliamperes. The operating conditions would not, as in A and B, be determined by variation of such great mag:

nitude proportionately, but by an increase or decrease of perhaps 20 percent in current flow as between no beam and high beam.

1 have found that particular designs of receivers have different characteristics as to the suitability of the connection at C. Whereas a 20 percent variation of B plus current into the damper tube was found in some designs, in others the characteristics in toto of the horizontal output stage seemed to reduce this percentage 21 great deal, while in still others a variation as high as 50 percent occurs.

However, where it is possible to use the C connection, this has the advantage that a magnetic field for actuating an electro-mechanical embodiment, or for application of the saturable reactor principle, may be obtained with a coil of many less turns-the ratio of current being 1,000 to 1 app. (as contrasted with the A and B forms).

It is in order, at this point, to call attention to the variety of heating voltages now in standard use. High- 'voltage rectifier tubes may be anywhere from a nominal 1.4 volt to a nominal 6.3 volt type. Their heating currents also vary widely and also their Wattages.

Also, the design of known transformers may have, for example, a six turn heater winding providing a nominal six volts, or the same nominal voltage may come from a two-turn winding.

It is therefore not possible to say, in connection with this invention, that a certain change is required in the winding of a transformer, for the benefits of the invention to be enjoyed. However, it is possible to say that, with the addition of a variable reactance coil 14, for example, in series with the heater 8 and heater winding 6, it will be necessary to add turns, or otherwise increase the coupling of the winding 6, so that the overall heating voltage (nominal) will be increased, so that the variable reactance coil 14 will have a certain amount of voltage to play with.

Consideration of the tolerance limits given by vacuum tube manufacturers for high-voltage rectifiers tells us that the tube should operate, in the case of 6.3 volt tubes:

For beam currents of O to 200 microamperes,

Vh equals 6.3 v. plus-minus 15 percent For beam currents of 200 microamperes and over, Vh equals 6.3 v. plus-minus 7 percent Analyzing the above, a little, it would follow that the voltage supplied to the tube should be No more than 6.3 v. plus .95 v. equals 7.25 (no load) No less than 6.3 v. minus .45 v. equals 5.85 (high beam) According to that standard, a variation of 1.4 volts is tolerable.

However, returning with these figures to the question of increasing the voltage output from a heating winding in order to have a surplus on hand to be reduced by a greater or lesser amount, and in the end more within the tolerance limits of the tube (which is the theory of this invention) I find that, for example, in using a 6.3 v. tube:

Increasing the transformer output to a (no load) 8.5 volts, and reducing that by 2 volts across a series reactance we would have 6.5 volts (no load). Now, as loading across the rectifier tube reached the maximum brightness range, and the transformer now produced 6.5 volts-if we are able to reduce our series reactance so that the drop across it is now .5 volt, we still have 6 volts supplied to the rectifier.

In other words, once the principle of compensation is adopted, it is possible to bring the operating conditions well within the tolerance limits. It is also possible to over-compensate, if the range of the compensating element or elements is sufficient, and instead of the familiar dimming out of a high-voltage rectifier tube as brilliance rises on the cathode-ray tube face it could be achieved that the rectifier would brighten the greater the demand for current from it (within limits, of course).

Let us consider now the known practice of inserting a series resistor in the rectifier heating circuit. One may presume that in the process of developing a new model of a receiver a transformer is constructed and tried in relation to the receiver, and with various samples of highvoltage rectifier tubes. Measurement of the heating voltage for such rectifiers, as is well known in the trade, is extremely difiicult. It is therefore common practice to rely on observation of the color and the brightness of the heater as a criterion. Still, in the last analysis, the proof of the pudding is in the eating. If, after extensive operational tests it is found that the high-voltage rectifier tube heaters tend to burn out (open circuit) it is decided to try a certain value of series resistor. Again, another value is tried. With low emission faults obtaining efforts are made to increase the voltage.

It will be seen that this is a dodgy business. A whole production run may go out, and even be sold, before it is realized that a touch more, or less, voltage is required; not to obtain many years of rectifier tube life, but just to obtain the present general average of performance.

Many millions of receivers do have a resistor in them, in series with the high-voltage rectifier tubes heater. There is no advantage in using such a resistance; it represents a compromise addition of a fractional amount added to the lump sum of impedance across the heater winding. And, since the resistor does not vary as beam current varies, it has no value as a compensating arrangement such as my invention provides.

The invention could use insertion, and withdrawal, dependent on beam current levels, of a fixed resistor, or a number of resistances, in series with the high-voltage rectifier tubes heater, and by means actuated, for example, by an electro-magnetic coil such as the driving coil 18 of FIGURE 1.

Such an embodiment may also use a variable resistor, increasing by increments as beam current decreased and vice versa.

Another embodiment uses the variation of capacity to offset the variation of heater voltage. Such variation of capacity may also be combined avith inductive variation and/or resistance variation.

Still another embodiment utilizes variation of the coupling between the heater winding 6 and the field of the transformer 4. As current output rises in the beam circuit, or the B plus supply to the damper tube, coupling to the heater winding increases, for example, by movement away of an intervening vane.

My preferred embodiments, however, utilize the variation of a series inductance as a means of controlling the rectifiers heating current. I feel that this method offers a number of advantages: Simplicity; no problem of the make-and-break of contacts; small size possible with the use of high permeability cores now available; greater range of variation combined with ease of initial adjustment; lower cost; in some forms continuous variation over the full range of loading conditions; fewer mechanical problems.

Considering again the FIGURE 1, if we are to insert the driving coil 18 at A, certain advantages will accrue, as against points B, or C. The greatest advantage is that the whole arrangement may be held at high-voltage potential, that is, for example, at 15 kv. DC. in relation to the chassis.

In one form, the customary lead 7 from the high-voltage rectifier heater. 8 to the final anode 9 of the cathoderay goes instead to a driving coil 18 which could be mounted on the output transformer and share the same high potential insulating material. Or, where the rectifier tube is mounted separately, for example has its own pedestal, the driving coil could be mounted thereon. A second connection would then supply the cathode-ray tube anode.

The variable reactance coil 14 would be able to be mounted close by, and a short coupling arrangement be used so that the core 17 of the driving coil drawing in to the driving coil 18 directly pulled a core 15 away from the reactance coil 14, and reduction of current results in a reverse movement due to a spring and/ or gravity.

The reactance coil connection only requires diversion of one lead from the customary rectifier tubes heater connection, with the other lead from the reactance coil taking its place. Both cores may be connected to the high-voltage D.C. point, and all elements in the system would then be equipotential.

I have made a model and obtained a compensating effect. I have included a drawing of the embodiment so constructed experimentally, and that is the drawing of FIGURE 4.

However, it should be understood that I believe this FIGURE 4 to be an awkward embodiment, and unable to provide continuous variation and control over the operating range of a high-voltage supply system. That is, it represents a method of two-state compensation, a lump sum of inductance is inserted, and withdrawn, with some degree of slope obtainable in between.

That model comprised a 40,000 ohm relay coil 19, an armature 20 which was attracted to the above relay coil when a current of about 50 to 100 microamperes was flowing in the beam current circuit, a small core 21 reduced in length from a type commonly used in width coils, and a variable reactance coil 22 of about 50 turns of No. 30 wire on a inch former.

By observation, I should estimate that I obtained a 1 volt variation-that is, when the rectifier, on low beam current, burned most brightly, I was able by insertion of the core 21 into the reactance coil 22 to reduce that brightness by what appeared to be 1 volt approximately. I had added, initially, two more turns to a six turn heater winding.

As beam current rose to 50 to 100 microamperes, I could, with various spacings of the movable armature 20 to the fixed armature 23 of the so-called relay coil, obtain a pull-up which removed the core 21 from the variable reactance coil 22 and the rectifier tube then increased in brilliance.

I also succeeded in obtaining movement of an armature, despite the very weak current, by using a 20,000 ohm relay coil.

While working on this model I came upon a group of ideas in relation to how to obtain the desired variation of an inductive reactance by means of a limited amount of movement. Recognizing that this constituted another invention, with many applications, I filed an application for British patent accompanied by a provisional specification on July 18, 1957, under the title Improvements in Variable Inductance Devices, which application was given the number 22853/57.

Persons skilled in the art will recognize that, given a certain amount of direct current, and .a variation of that amount from zero to the maximum, design of a suitable application arrangement for utilizing the magnetic field obtainable is a question of ampere-turns, size of wire, permeability, weight of armature, tension of springs and effect of gravity, etc. Modern industry will solve the problem of how to produce various applications of my principles.

I believe, however, that I am the first to use the current through a cathode-ray tube (beam current) to do work in addition to its primary function.

Even though crude, the embodiment I built could be added to a television receiver at a cost of about a dollar. With high-voltage rectifier tubes costing about two dollars each, and with service charges which can amount to several dollars more, even if a 40,000 ohm coil were required for the driving coil, that would still be desirable economically. Further, there is the question of loss of use of the TV set during breakdowns.

It is known that magnetic attraction varies inversely as the square of the distance. Thus the movement in any electro-mechanical embodiment will not have a straight line characteristic unless the opposing force (spring and/ or gravity) varies by the square of the distance traversed, or something of the sort. There is a wealth of prior art on this subject, it is not my province.

Movement may be linear (in a physical sense), or it could be along a curve. In the embodiment of FIGURE 4, as constructed by me, movement describes an are, an armature being suspended from supports and bearing surfaces and a pendulum-type motion occurs when magnetic attraction overcomes gravity, inertia and friction.

Since the heating current for high-voltage rectifier tubes is derived from a complex wave-form current in the other windings of a horizontal output transformer, having a fundamental frequency of 15,750 c.p.s. in 525 line systems (10,125 c.p.s. in 405 line systems) plus a great many harmonics, I found experimentally that a powdered iron core of high permeability appeared to be better suited for the core of the variable reactance coil than a solid iron core. There was also thefproblem, apparently, of absorption of energy, probably due to eddy currents, and the system has little enough energy to spare.

How successful a designer will be in theoretically determining what size and other characteristics of coil to use with What core, in developing a particular application of this invention, I do not know. One designer remarked that the wave-form was so complex it was not possible to see it on an oscilloscope, and the only solution would be trial and error. That method has solved many problems.

Saturable reactors are used now for another part of a horizontal output systemthey serve, in some cases, as linearity controls, the principle there being that the instanteous impedance in a circuit varies according to the current flowing, and becomes less as the current increases beyond a certain level, controllable by a permanent magnet movable in relation to a saturable core.

Here we are not concerned with the instantaneous level of current flow, so far as the heater current is concerned, but rather we Wish to increase and decrease an inductive reactance so that, on the average, the heater current will tend to increase with beam current.

An off-hand remark by another designer indicated concern over the prospect of attempting to obtain saturation from a current as weak as the beam current through a cathode-ray tube. For him the solution lay in using the connection C of FIGURE 1, with its thousand times greater current.

I feel that beam current can serve to produce saturation, provided that the field developed is concentrated sufficiently on a very small core, which core is highly efficient as a means of controlling the reactance of a small coil-the impedance of which needs to be varied only by a small amounta few ohms will be highly effective. A one-volt variation, for nominal 6 volt heaters, controlled by beam current, can solve most highvoltage rectifier tube failures.

I therefore describe and illustrate in FIGURE 2 an embodiment in which the relatively large number of turns of wire of the coil 24 through which the beam current flows concentrates its field on a thin core 25 on which is wound a few turn coil 26 in series with the heating circuit of the high-voltage rectifier tube. Relative to this combination there is a permanent magnetic mass 27 Which may be adjustable, and which serves to provide an initial polarization to which the beam current adds.

Such an arrangement could perhaps be reduced in size to about one cubic inch, and be a small addition to a horizontal output transformer assembly.

The same principle may be applied in other forms, and the connection may be at A, B or C.

A modification combining both principles, electromechanical and saturable reactor, is illustrated in FIG- URE 3. Here a single core 28 is shared by the driving coil 29 and the variable reactance coil 30. Increased magnetism with increase of beam current not only draws the core 28 into the driving coil and out of the reactance coil, but it also increases the polarization of the core reducing its effectiveness as a core for the reactance coil.

This embodiment may also take such forms as, for example, a diaphragm between two coils; or, a pendulum shaped like a traditional ships anchor, with both movement and polarization; or, a pivoted vane such as are used in moving-vane meters.

FIGURE illustrates an embodiment in which the variation of bias voltage, between the control grid 31 and the cathode 32 of the cathode-ray tube, is utilized to control the emission through a vacuum tube 33. That controlled emission, the current from cathode to plate of vacuum tube 33 is then applied by well known means to the task of operating any of the embodiments of the invention previously described, this current being used in place of beam current of B plus supply current to the damper tube.

The operating levels of vacuum tube 33 may be set so that neither cut-off nor saturation are reached, and continuous compensation is achieved. It will be noted that by applying a reduced portion of the voltages from both cathode 32 and control grid 31 of the cathode-ray tube to the cathode 34 and control grid 35 of the vacuum tube 33, any variation of bias, whether due to modulation or to adjustment of brilliance level, results in changes at the vacuum tubes plate 36, and thereby at the high-voltage rectifiers heater circuit.

The whole principle of the invention being new, the embodiments described are not presumed to exhaust the possibilities. However, examples given establish the basis for a number of broad claims.

I claim:

1. A compensating circuit for a high voltage supply system comprising in combination a voltage transformer, a high voltage output winding on said transformer, a rectifier tube connected to said high voltage output winding to rectify the output therefrom, a cathode heating circuit for said rectifier tube, a low voltage output winding on said transformer, connections from said low voltage output winding to said cathode heating circuit, an inductive element in said heating circuit, and, means responsive to current flow through said rectifier tube and adapted to regulate the inductance of said inductive element.

2. A compensating circuit for a high voltage supply system comprising in combination a voltage transformer, a high voltage output winding on said transformer, a rectifier tube connected to said high voltage output winding to rectify the output therefrom, a cathode heating circuit for said rectifier tube, a low voltage output winding on said transformer, connections from said low voltage output winding to said cathode heating circuit, an inductive element in said heating circuit, a magnetic material core in said inductive element, and, means responsive to current flow through said rectifier tube adapted to vary the degree of magnetic saturation of said magnetic material core.

References Cited in the file of this patent UNITED STATES PATENTS 684,342 Baker Oct. 8, 1901 1,961,703 Morrison June 5, 1934 2,188,290 Von Ardenne Jan. 23, 1940 2,412,682 Hershberger Dec. 17, 1946 2,644,104 Fyler June 30, 1953 2,697,798 Schlesinger Dec. 21, 1954 2,790,108 Bigelow Apr. 23, 1957 2,793,322 Tourshou May 21, 1957 2,810,838 Clapp Oct. 22, 1957 2,830,230 Fyler Apr. 8, 1958 2,833,961 Thalner May 6, 1958 2,863,113 Ehret Dec. 2, 1958 2,888,607 Hooper May 26, 1959 

1. A COMPENSATING CIRCUIT FOR A HIGH VOLTAGE SUPPLY SYSTEM COMPRISING IN COMBINATION A VOLTAGE TRANSFORMER, A HIGH VOLTAGE OUTPUT WINDING ON SAID TRANSFORMER, A RECTIFIER TUBE CONNECTED TO SAID HIGH VOLTAGE OUTPUT WINDING TO RECTIFY THE OUTPUT THEREFROM, A CATHODE HEATING CIRCUIT FOR SAID RECTIFIER TUBE, A LOW VOLTAGE OUTPUT WINDING ON SAID TRANSFORMER, CONNECTIONS FROM SAID LOW VOLTAGE OUTPUT WINDING TO SAID CATHODE HEATING CIRCUIT, AN INDUCTIVE ELEMENT IN SAID HEATING CIRCUIT, AND, MEANS RESPONSIVE TO CURRENT FLOW THROUGH SAID RECTIFIER TUBE AND ADAPTED TO REGULATE THE INDUCTANCE OF SAID INDUCTIVE ELEMENT. 